1. Field of the Invention
The present invention relates to a polymer composition for an inner liner, and a pneumatic tire using the same.
2. Description of the Background Art
Recently, an attempt has been made to perform weight saving of tires because of strong social demands for fuel economy of automobiles. An attempt has also been made to perform weight saving of inner liners, among tire members, that are disposed inside tires and have the function of improving air permeation resistance by decreasing the amount of air leaked to the outside from the inside of pneumatic tires (air permeation amount).
In a rubber composition for an inner liner, an improvement in air permeation resistance of tires is performed by using a butyl-based rubber containing 70 to 100% by mass of a butyl rubber and 30 to 0% by mass of a natural rubber. The butyl-based rubber contains, in addition to butylene, about 1% by mass of isoprene, that enables cocrosslinking with an adjacent rubber along with sulfur, a vulcanization accelerator and zinc white. In the case of a conventional formulation, the butyl-based rubber requires the thickness of about 0.6 to 1.0 mm for tires for passenger cars, or the thickness of about 1.0 to 2.0 mm for trucks and buses. In order to perform weight saving of tires, there is proposed a polymer which is more excellent in air permeation resistance than the butyl-based rubber and can further decrease the thickness of the inner liner layer.
Japanese Patent Laying-Open No. 2007-291256 proposes, as a pneumatic tire that can simultaneously realize suppression of air pressure drop, improvement in durability and improvement in fuel efficiency, a pneumatic tire using a rubber composition for an inner liner, containing an ethylene-vinyl alcohol copolymer represented by the following general formula (1):
wherein m and n each independently represent 1 to 100 and x represents 1 to 1000, in the amount within a range from 15 to 30 parts by mass based on 100 parts by mass of a rubber component composed of a natural rubber and/or a synthetic rubber, in an inner liner layer. However, the technique of Japanese Patent Laying-Open No. 2007-291256 leaves much room for improvement in respect of weight saving of tires since a rubber sheet using the rubber composition has a thickness of 1 mm.
Japanese Patent Laying-Open No. 09-165469 proposes a pneumatic tire in which adhesion between an inner liner and a rubber composition constituting the inner surface of the tire or a carcass layer can be improved by forming an inner liner layer using nylon with low air permeability. However, the technique of Japanese Patent Laying-Open No. 09-165469 has a problem that a rubber cement composed of a rubber composition must be bonded after subjecting a nylon film to an RFL treatment so as to form a nylon film layer, resulting in complicated steps.